The National Weather Service issues a structured set of marine alerts based on observed and forecast wind, sea state, and visibility. The most relevant ones for inland-lake sailors are:
- Small Craft Advisory. Sustained winds of 18–33 kt or seas/waves expected to be challenging for small boats. The exact threshold varies by NWS forecast office and water body. On inland lakes the wind threshold typically kicks in at 20 kt sustained.
- Special Marine Warning. A short-fused warning (usually less than two hours) for severe convective weather over water — thunderstorms with winds over 34 kt or hail. These often precede or accompany Severe Thunderstorm Warnings on the adjacent land.
- Lake Wind Advisory. Used by some Great Lakes and Western forecast offices for sustained winds of 25–35 kt. Common on Lake Tahoe, Lake Mendota, Lake Hefner.
- Gale Warning. 34–47 kt. Beyond small-craft territory.
- Storm Warning, Hurricane Force Warning. Stronger.
- Severe Thunderstorm Watch / Warning, Tornado Watch / Warning. Atmospheric, not marine, but Lakebrief surfaces them too because they affect the decision to launch.
Lakebrief pulls active alerts from api.weather.gov/alerts/active?point=<lat,lon> for every lake's coordinates and merges them into the alert ribbon and the per-lake Alerts page. NWS designates each alert with a severity (Extreme / Severe / Moderate / Minor / Unknown) and Lakebrief maps those to its own three-tier model: warning / advisory / info.
Two important caveats:
Inland lakes get fewer marine alerts than the coast. NWS forecast zones for marine alerts are defined for navigable waters — primarily the coast, the Great Lakes, and major inland waterways. Smaller inland lakes are usually covered by the surrounding land's forecast zone, which means you'll see Severe Thunderstorm Warnings and Wind Advisories but not always a Small Craft Advisory specifically. The dashboard shows whatever NWS publishes for the coordinates; absence of a "marine" alert doesn't mean absence of severe weather.
Some advisories are Spanish-language duplicates. NWS publishes a parallel Spanish version of many alerts. Lakebrief shows them all rather than dedupe — a Spanish-speaking sailor benefits from seeing the original. The Alerts page renders each in its source language.
For decision-making, the rule of thumb is: if NWS has a Small Craft Advisory, Severe Thunderstorm Warning, or Special Marine Warning active for your lake, don't launch. The advisory exists because the local forecaster looked at radar, model data, and observations and made a call. That call is more informed than any number on a dashboard.